1. Field of the Invention
This invention relates to a printing head for applying an image-responsive electrical signal to a printing medium.
2. Description of the Prior Art
A printing method, known as electric transfer printing, has been proposed in which an image-responsive electrical signal is changed into heat to melt an ink layer and transfer it to paper, thereby forming an image.
One printing head for such a method comprises integral printing electrodes and return electrodes. Each of the return electrodes has a greater contact area than each of the printing electrodes. (See, for example, Japanese Patent Application (OPI) No. 171666/84 (the term "OPI" as used herein means an "unexamined published application")). Other proposed printing heads include one comprising printing electrodes formed of a metal layer patterned on a ceramic board, or one comprising a lamination of printing electrode materials and ceramic materials.
In the printing head of the former type, the printing electrodes and the return electrodes are provided on a surface which is put in contact with a printing medium, so that the pressure contact area of the printing head is large. For this reason, the total contact pressure needs to be high, which not only makes it difficult to apply a uniform pressure but also requires a large torque for driving rollers. As a result, the reliability of printing performance is low.
To make an image recording with the printing head of the latter type, it is required that an end portion of the surface of the printing head be in surface contact with the printing medium. This means that any inclination of the printing head toward the printing medium drastically impairs the contact ratio. Hence, the printing head must always be maintained parallel to the printing medium, which imposes the problem of requiring a highly accurate printing head holding mechanism.